Take a look here in this post : http://www.insanelymac.com/forum/topic/281665-nforce-os-x-mountain-lion-108-app-store-download-install-guide-on-a-series-6-or-7-nforce-chipset-intel-cpu-mobo/?do=findComment&comment=1842802
and here more info: http://www.google.com/cse?cx=015502606800201147678%3Aghutp5a8jhi&ie=UTF-8&q=#gsc.tab=0&gsc.q=9800gt%20maverick&gsc.sort=